Added image downsampling/compression

Reviewed-on: buzzert/smartbar#8

Makefile

@@ -27,6 +27,8 @@ serve: deps
 
 PDF := $(OUT_DIR)/output.pdf
 PDF_2UP := $(OUT_DIR)/output-2up.pdf
+PDF_IMAGE_DPI ?= 144
+PDF_JPEG_QUALITY ?= 75
 
 .PHONY: deps
 deps:
@@ -35,13 +37,12 @@ deps:
 .PHONY: pdf
 pdf: build deps
 	@echo "Generating PDF by rendering each page and merging..."
-	@$(GO) run ./cmd/pdfbook --pages $(OUT_DIR) --order pages.yaml --out $(PDF)
+	@$(GO) run ./cmd/pdfbook --pages $(OUT_DIR) --order pages.yaml --out $(PDF) --image-dpi $(PDF_IMAGE_DPI) --jpeg-quality $(PDF_JPEG_QUALITY)
 
 .PHONY: pdf-2up
 pdf-2up: build deps
 	@echo "Generating 2-up PDF with headless Chrome..."
-	@$(GO) run ./cmd/pdf --in $(OUT_DIR)/print_2up.html --out $(PDF_2UP) --w 11 --h 8.5
+	@$(GO) run ./cmd/pdf --in $(OUT_DIR)/print_2up.html --out $(PDF_2UP) --w 11 --h 8.5 --image-dpi $(PDF_IMAGE_DPI) --jpeg-quality $(PDF_JPEG_QUALITY)
 
 clean:
 	rm -rf $(OUT_DIR) index.html
-

cmd/pdf/main.go

@@ -10,6 +10,7 @@ import (
 	"path/filepath"
 
 	"smartbar/internal/config"
+	"smartbar/internal/pdfassets"
 
 	"github.com/chromedp/cdproto/emulation"
 	"github.com/chromedp/cdproto/page"
@@ -38,15 +39,19 @@ func findChromeExec() (string, error) {
 
 func main() {
 	var (
-		input  string
-		output string
-		width  float64
-		height float64
+		input       string
+		output      string
+		width       float64
+		height      float64
+		imageDPI    int
+		jpegQuality int
 	)
 	flag.StringVar(&input, "in", "", "input HTML file path (required)")
 	flag.StringVar(&output, "out", "", "output PDF path (required)")
 	flag.Float64Var(&width, "w", config.PageWidthIn, "page width in inches")
 	flag.Float64Var(&height, "h", config.PageHeightIn, "page height in inches")
+	flag.IntVar(&imageDPI, "image-dpi", 144, "downsample image assets to this PDF pixel density; 0 disables")
+	flag.IntVar(&jpegQuality, "jpeg-quality", 75, "JPEG quality for PDF image assets")
 	flag.Parse()
 
 	if input == "" || output == "" {
@@ -54,6 +59,32 @@ func main() {
 	}
 
 	absInput, _ := filepath.Abs(input)
+	inputRoot := filepath.Dir(absInput)
+	inputRel := filepath.Base(absInput)
+	imageOpts := pdfassets.OptionsForPage(width, height, imageDPI, jpegQuality)
+	prepared, err := pdfassets.PrepareTree(inputRoot, imageOpts)
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer func() {
+		if err := prepared.Cleanup(); err != nil {
+			log.Printf("warning: cleanup optimized PDF assets: %v", err)
+		}
+	}()
+	if prepared.Stats.ImageFiles > 0 {
+		fmt.Printf(
+			"Optimized PDF images: %d/%d files, %s -> %s (max %dx%d, JPEG quality %d)\n",
+			prepared.Stats.OptimizedImages,
+			prepared.Stats.ImageFiles,
+			pdfassets.FormatBytes(prepared.Stats.OriginalBytes),
+			pdfassets.FormatBytes(prepared.Stats.OutputBytes),
+			imageOpts.MaxWidth,
+			imageOpts.MaxHeight,
+			imageOpts.JPEGQuality,
+		)
+	}
+
+	absInput = filepath.Join(prepared.Root, inputRel)
 	url := "file://" + absInput
 
 	execPath, err := findChromeExec()

cmd/pdfbook/main.go

@@ -1,158 +1,183 @@
 package main
 
 import (
-    "context"
-    "flag"
-    "fmt"
-    "log"
-    "os"
-    "os/exec"
-    "path/filepath"
-    "strings"
+	"context"
+	"flag"
+	"fmt"
+	"log"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
 
-    "smartbar/internal/config"
+	"smartbar/internal/config"
+	"smartbar/internal/pdfassets"
 
-    "github.com/chromedp/cdproto/emulation"
-    "github.com/chromedp/cdproto/page"
-    "github.com/chromedp/chromedp"
-    pdfapi "github.com/pdfcpu/pdfcpu/pkg/api"
+	"github.com/chromedp/cdproto/emulation"
+	"github.com/chromedp/cdproto/page"
+	"github.com/chromedp/chromedp"
+	pdfapi "github.com/pdfcpu/pdfcpu/pkg/api"
 )
 
 func must(err error) {
-    if err != nil {
-        log.Fatal(err)
-    }
+	if err != nil {
+		log.Fatal(err)
+	}
 }
 
 func parseYAMLListOfStrings(src string) ([]string, error) {
-    var out []string
-    for _, line := range strings.Split(src, "\n") {
-        line = strings.TrimSpace(line)
-        if line == "" || strings.HasPrefix(line, "#") {
-            continue
-        }
-        if strings.HasPrefix(line, "-") {
-            item := strings.TrimSpace(strings.TrimPrefix(line, "-"))
-            if item != "" {
-                out = append(out, item)
-            }
-        } else {
-            return nil, fmt.Errorf("invalid yaml line (expect '- item'): %s", line)
-        }
-    }
-    return out, nil
+	var out []string
+	for _, line := range strings.Split(src, "\n") {
+		line = strings.TrimSpace(line)
+		if line == "" || strings.HasPrefix(line, "#") {
+			continue
+		}
+		if strings.HasPrefix(line, "-") {
+			item := strings.TrimSpace(strings.TrimPrefix(line, "-"))
+			if item != "" {
+				out = append(out, item)
+			}
+		} else {
+			return nil, fmt.Errorf("invalid yaml line (expect '- item'): %s", line)
+		}
+	}
+	return out, nil
 }
 
 func findChromeExec() (string, error) {
-    if v := os.Getenv("CHROME_PATH"); v != "" {
-        return v, nil
-    }
-    candidates := []string{"google-chrome-stable", "google-chrome", "chromium-browser", "chromium", "chrome"}
-    for _, name := range candidates {
-        if p, err := exec.LookPath(name); err == nil {
-            return p, nil
-        }
-    }
-    // macOS common app bundle paths
-    macPaths := []string{
-        "/Applications/Google Chrome.app/Contents/MacOS/Google Chrome",
-        "/Applications/Google Chrome Canary.app/Contents/MacOS/Google Chrome Canary",
-        "/Applications/Chromium.app/Contents/MacOS/Chromium",
-    }
-    for _, p := range macPaths {
-        if _, err := os.Stat(p); err == nil {
-            return p, nil
-        }
-    }
-    return "", fmt.Errorf("no Chrome/Chromium executable found; set CHROME_PATH or install chromium/google-chrome")
+	if v := os.Getenv("CHROME_PATH"); v != "" {
+		return v, nil
+	}
+	candidates := []string{"google-chrome-stable", "google-chrome", "chromium-browser", "chromium", "chrome"}
+	for _, name := range candidates {
+		if p, err := exec.LookPath(name); err == nil {
+			return p, nil
+		}
+	}
+	// macOS common app bundle paths
+	macPaths := []string{
+		"/Applications/Google Chrome.app/Contents/MacOS/Google Chrome",
+		"/Applications/Google Chrome Canary.app/Contents/MacOS/Google Chrome Canary",
+		"/Applications/Chromium.app/Contents/MacOS/Chromium",
+	}
+	for _, p := range macPaths {
+		if _, err := os.Stat(p); err == nil {
+			return p, nil
+		}
+	}
+	return "", fmt.Errorf("no Chrome/Chromium executable found; set CHROME_PATH or install chromium/google-chrome")
 }
- 
+
 func main() {
-    var (
-        pagesDir string
-        orderPath string
-        outPDF string
-        width  float64
-        height float64
-    )
-    flag.StringVar(&pagesDir, "pages", "_dist", "path to compiled pages directory (required)")
-    flag.StringVar(&orderPath, "order", "pages.yaml", "path to YAML file listing page order (required)")
-    flag.StringVar(&outPDF, "out", "_dist/output.pdf", "output PDF path (required)")
-    flag.Float64Var(&width, "w", config.PageWidthIn, "page width in inches")
-    flag.Float64Var(&height, "h", config.PageHeightIn, "page height in inches")
-    flag.Parse()
+	var (
+		pagesDir    string
+		orderPath   string
+		outPDF      string
+		width       float64
+		height      float64
+		imageDPI    int
+		jpegQuality int
+	)
+	flag.StringVar(&pagesDir, "pages", "_dist", "path to compiled pages directory (required)")
+	flag.StringVar(&orderPath, "order", "pages.yaml", "path to YAML file listing page order (required)")
+	flag.StringVar(&outPDF, "out", "_dist/output.pdf", "output PDF path (required)")
+	flag.Float64Var(&width, "w", config.PageWidthIn, "page width in inches")
+	flag.Float64Var(&height, "h", config.PageHeightIn, "page height in inches")
+	flag.IntVar(&imageDPI, "image-dpi", 144, "downsample image assets to this PDF pixel density; 0 disables")
+	flag.IntVar(&jpegQuality, "jpeg-quality", 75, "JPEG quality for PDF image assets")
+	flag.Parse()
 
-    if pagesDir == "" || orderPath == "" || outPDF == "" {
-        log.Fatal("--pages, --order and --out are required")
-    }
+	if pagesDir == "" || orderPath == "" || outPDF == "" {
+		log.Fatal("--pages, --order and --out are required")
+	}
 
-    // Load order
-    data, err := os.ReadFile(orderPath)
-    must(err)
-	
-    ordered, err := parseYAMLListOfStrings(string(data))
-    must(err)
+	// Load order
+	data, err := os.ReadFile(orderPath)
+	must(err)
 
-    // Resolve Chrome
-    chromeExec, err := findChromeExec()
-    must(err)
-	
-    opts := append(chromedp.DefaultExecAllocatorOptions[:], chromedp.ExecPath(chromeExec), chromedp.Flag("headless", true), chromedp.Flag("disable-gpu", true), chromedp.Flag("hide-scrollbars", true))
-    allocCtx, cancel := chromedp.NewExecAllocator(context.Background(), opts...)
-    defer cancel()
+	ordered, err := parseYAMLListOfStrings(string(data))
+	must(err)
 
-    ctx, cancel := chromedp.NewContext(allocCtx)
-    defer cancel()
+	imageOpts := pdfassets.OptionsForPage(width, height, imageDPI, jpegQuality)
+	prepared, err := pdfassets.PrepareTree(pagesDir, imageOpts)
+	must(err)
+	defer func() {
+		if err := prepared.Cleanup(); err != nil {
+			log.Printf("warning: cleanup optimized PDF assets: %v", err)
+		}
+	}()
+	pagesDir = prepared.Root
+	if prepared.Stats.ImageFiles > 0 {
+		fmt.Printf(
+			"Optimized PDF images: %d/%d files, %s -> %s (max %dx%d, JPEG quality %d)\n",
+			prepared.Stats.OptimizedImages,
+			prepared.Stats.ImageFiles,
+			pdfassets.FormatBytes(prepared.Stats.OriginalBytes),
+			pdfassets.FormatBytes(prepared.Stats.OutputBytes),
+			imageOpts.MaxWidth,
+			imageOpts.MaxHeight,
+			imageOpts.JPEGQuality,
+		)
+	}
 
-    // Temp dir for individual PDFs
-    tmpDir, err := os.MkdirTemp("", "smartbar_pdfs_*")
-    must(err)
-    defer os.RemoveAll(tmpDir)
+	// Resolve Chrome
+	chromeExec, err := findChromeExec()
+	must(err)
 
-    var partPDFs []string
-    for _, rel := range ordered {
-        abs := filepath.Join(pagesDir, rel)
-        if _, err := os.Stat(abs); err != nil {
-            log.Printf("skip missing page: %s", rel)
-            continue
-        }
-        absHTML, _ := filepath.Abs(abs)
-        url := "file://" + absHTML
+	opts := append(chromedp.DefaultExecAllocatorOptions[:], chromedp.ExecPath(chromeExec), chromedp.Flag("headless", true), chromedp.Flag("disable-gpu", true), chromedp.Flag("hide-scrollbars", true))
+	allocCtx, cancel := chromedp.NewExecAllocator(context.Background(), opts...)
+	defer cancel()
 
-        outPath := filepath.Join(tmpDir, strings.TrimSuffix(filepath.Base(rel), filepath.Ext(rel)) + ".pdf")
-        // Render one page PDF via printToPDF
-        err := chromedp.Run(ctx, chromedp.Tasks{
-            chromedp.Navigate(url),
-            chromedp.ActionFunc(func(ctx context.Context) error {
-                if err := emulation.SetEmulatedMedia().WithMedia("print").Do(ctx); err != nil {
-                    return err
-                }
-                params := page.PrintToPDF().
-                    WithPaperWidth(width).
-                    WithPaperHeight(height).
-                    WithMarginTop(0).WithMarginBottom(0).WithMarginLeft(0).WithMarginRight(0).
-                    WithPrintBackground(true)
-                buf, _, err := params.Do(ctx)
-                if err != nil {
-                    return err
-                }
-                return os.WriteFile(outPath, buf, 0o644)
-            }),
-        })
-        must(err)
-        partPDFs = append(partPDFs, outPath)
-    }
+	ctx, cancel := chromedp.NewContext(allocCtx)
+	defer cancel()
 
-    if len(partPDFs) == 0 {
-        log.Fatal("no pages produced; check order file")
-    }
+	// Temp dir for individual PDFs
+	tmpDir, err := os.MkdirTemp("", "smartbar_pdfs_*")
+	must(err)
+	defer os.RemoveAll(tmpDir)
 
-    // Merge PDFs into single output
-    must(os.MkdirAll(filepath.Dir(outPDF), 0o755))
+	var partPDFs []string
+	for _, rel := range ordered {
+		abs := filepath.Join(pagesDir, rel)
+		if _, err := os.Stat(abs); err != nil {
+			log.Printf("skip missing page: %s", rel)
+			continue
+		}
+		absHTML, _ := filepath.Abs(abs)
+		url := "file://" + absHTML
 
-    // pdfcpu expects []string in order and writes outPDF
-    must(pdfapi.MergeCreateFile(partPDFs, outPDF, false, nil))
-    fmt.Printf("Wrote %s (%d pages)\n", outPDF, len(partPDFs))
+		outPath := filepath.Join(tmpDir, strings.TrimSuffix(filepath.Base(rel), filepath.Ext(rel))+".pdf")
+		// Render one page PDF via printToPDF
+		err := chromedp.Run(ctx, chromedp.Tasks{
+			chromedp.Navigate(url),
+			chromedp.ActionFunc(func(ctx context.Context) error {
+				if err := emulation.SetEmulatedMedia().WithMedia("print").Do(ctx); err != nil {
+					return err
+				}
+				params := page.PrintToPDF().
+					WithPaperWidth(width).
+					WithPaperHeight(height).
+					WithMarginTop(0).WithMarginBottom(0).WithMarginLeft(0).WithMarginRight(0).
+					WithPrintBackground(true)
+				buf, _, err := params.Do(ctx)
+				if err != nil {
+					return err
+				}
+				return os.WriteFile(outPath, buf, 0o644)
+			}),
+		})
+		must(err)
+		partPDFs = append(partPDFs, outPath)
+	}
+
+	if len(partPDFs) == 0 {
+		log.Fatal("no pages produced; check order file")
+	}
+
+	// Merge PDFs into single output
+	must(os.MkdirAll(filepath.Dir(outPDF), 0o755))
+
+	// pdfcpu expects []string in order and writes outPDF
+	must(pdfapi.MergeCreateFile(partPDFs, outPDF, false, nil))
+	fmt.Printf("Wrote %s (%d pages)\n", outPDF, len(partPDFs))
 }
-
-

go.mod

@@ -9,6 +9,7 @@ require (
 	github.com/chromedp/chromedp v0.9.5
 	github.com/fsnotify/fsnotify v1.9.0
 	github.com/pdfcpu/pdfcpu v0.11.0
+	golang.org/x/image v0.27.0
 )
 
 require (
@@ -25,7 +26,6 @@ require (
 	github.com/pkg/errors v0.9.1 // indirect
 	github.com/rivo/uniseg v0.4.7 // indirect
 	golang.org/x/crypto v0.38.0 // indirect
-	golang.org/x/image v0.27.0 // indirect
 	golang.org/x/sys v0.33.0 // indirect
 	golang.org/x/text v0.25.0 // indirect
 	gopkg.in/yaml.v2 v2.4.0 // indirect

internal/pdfassets/pdfassets.go

@@ -0,0 +1,470 @@
+package pdfassets
+
+import (
+	"bytes"
+	"encoding/binary"
+	"fmt"
+	"image"
+	stddraw "image/draw"
+	"image/jpeg"
+	"image/png"
+	"io"
+	"io/fs"
+	"math"
+	"os"
+	"path/filepath"
+	"strings"
+
+	xdraw "golang.org/x/image/draw"
+)
+
+type Options struct {
+	MaxWidth    int
+	MaxHeight   int
+	JPEGQuality int
+}
+
+type Stats struct {
+	ImageFiles      int
+	OptimizedImages int
+	OriginalBytes   int64
+	OutputBytes     int64
+}
+
+type PreparedTree struct {
+	Root    string
+	Stats   Stats
+	Cleanup func() error
+}
+
+func OptionsForPage(widthIn, heightIn float64, imageDPI, jpegQuality int) Options {
+	if imageDPI <= 0 {
+		return Options{JPEGQuality: clampJPEGQuality(jpegQuality)}
+	}
+	return Options{
+		MaxWidth:    max(1, int(math.Ceil(widthIn*float64(imageDPI)))),
+		MaxHeight:   max(1, int(math.Ceil(heightIn*float64(imageDPI)))),
+		JPEGQuality: clampJPEGQuality(jpegQuality),
+	}
+}
+
+func (o Options) Enabled() bool {
+	return o.MaxWidth > 0 && o.MaxHeight > 0
+}
+
+func PrepareTree(srcRoot string, opts Options) (PreparedTree, error) {
+	if !opts.Enabled() {
+		return PreparedTree{
+			Root:    srcRoot,
+			Cleanup: func() error { return nil },
+		}, nil
+	}
+
+	absRoot, err := filepath.Abs(srcRoot)
+	if err != nil {
+		return PreparedTree{}, err
+	}
+
+	tmpRoot, err := os.MkdirTemp("", "smartbar_pdf_assets_*")
+	if err != nil {
+		return PreparedTree{}, err
+	}
+
+	prepared := PreparedTree{
+		Root:    tmpRoot,
+		Cleanup: func() error { return os.RemoveAll(tmpRoot) },
+	}
+
+	err = filepath.WalkDir(absRoot, func(path string, d fs.DirEntry, walkErr error) error {
+		if walkErr != nil {
+			return walkErr
+		}
+
+		rel, err := filepath.Rel(absRoot, path)
+		if err != nil {
+			return err
+		}
+		if rel == "." {
+			return nil
+		}
+
+		dst := filepath.Join(tmpRoot, rel)
+
+		if d.IsDir() {
+			return os.MkdirAll(dst, 0o755)
+		}
+
+		info, err := d.Info()
+		if err != nil {
+			return err
+		}
+
+		if info.Mode()&fs.ModeSymlink != 0 {
+			return copySymlink(path, dst)
+		}
+
+		if !info.Mode().IsRegular() {
+			return nil
+		}
+
+		if strings.EqualFold(filepath.Ext(path), ".pdf") {
+			return nil
+		}
+
+		if isSupportedImage(path) {
+			stats, err := optimizeImageFile(path, dst, info.Mode().Perm(), opts)
+			if err == nil {
+				prepared.Stats.ImageFiles++
+				prepared.Stats.OriginalBytes += stats.originalBytes
+				prepared.Stats.OutputBytes += stats.outputBytes
+				if stats.optimized {
+					prepared.Stats.OptimizedImages++
+				}
+				return nil
+			}
+		}
+
+		return copyFile(path, dst, info.Mode().Perm())
+	})
+	if err != nil {
+		_ = prepared.Cleanup()
+		return PreparedTree{}, err
+	}
+
+	return prepared, nil
+}
+
+type imageFileStats struct {
+	originalBytes int64
+	outputBytes   int64
+	optimized     bool
+}
+
+func optimizeImageFile(src, dst string, mode fs.FileMode, opts Options) (imageFileStats, error) {
+	data, err := os.ReadFile(src)
+	if err != nil {
+		return imageFileStats{}, err
+	}
+
+	optimized, changed, err := optimizeImage(data, filepath.Ext(src), opts)
+	if err != nil {
+		return imageFileStats{}, err
+	}
+
+	if err := os.MkdirAll(filepath.Dir(dst), 0o755); err != nil {
+		return imageFileStats{}, err
+	}
+
+	output := optimized
+	if !changed {
+		output = data
+	}
+	if err := os.WriteFile(dst, output, mode); err != nil {
+		return imageFileStats{}, err
+	}
+
+	return imageFileStats{
+		originalBytes: int64(len(data)),
+		outputBytes:   int64(len(output)),
+		optimized:     changed,
+	}, nil
+}
+
+func optimizeImage(data []byte, ext string, opts Options) ([]byte, bool, error) {
+	img, format, err := image.Decode(bytes.NewReader(data))
+	if err != nil {
+		return nil, false, err
+	}
+
+	orientation := 1
+	if format == "jpeg" || strings.EqualFold(ext, ".jpg") || strings.EqualFold(ext, ".jpeg") {
+		orientation = jpegOrientation(data)
+		img = applyOrientation(img, orientation)
+	}
+
+	srcBounds := img.Bounds()
+	dstW, dstH := fitWithin(srcBounds.Dx(), srcBounds.Dy(), opts.MaxWidth, opts.MaxHeight)
+	resized := dstW != srcBounds.Dx() || dstH != srcBounds.Dy()
+	if resized {
+		dst := image.NewRGBA(image.Rect(0, 0, dstW, dstH))
+		xdraw.CatmullRom.Scale(dst, dst.Bounds(), img, srcBounds, stddraw.Src, nil)
+		img = dst
+	}
+
+	var buf bytes.Buffer
+	if imageHasTransparency(img) {
+		encoder := png.Encoder{CompressionLevel: png.BestCompression}
+		err = encoder.Encode(&buf, img)
+	} else {
+		err = jpeg.Encode(&buf, img, &jpeg.Options{Quality: clampJPEGQuality(opts.JPEGQuality)})
+	}
+	if err != nil {
+		return nil, false, err
+	}
+
+	changed := resized || orientation != 1 || buf.Len() < len(data)
+	if !changed {
+		return data, false, nil
+	}
+	return buf.Bytes(), true, nil
+}
+
+func fitWithin(width, height, maxWidth, maxHeight int) (int, int) {
+	if width <= 0 || height <= 0 || maxWidth <= 0 || maxHeight <= 0 {
+		return width, height
+	}
+	if width <= maxWidth && height <= maxHeight {
+		return width, height
+	}
+
+	scale := math.Min(float64(maxWidth)/float64(width), float64(maxHeight)/float64(height))
+	return max(1, int(math.Round(float64(width)*scale))), max(1, int(math.Round(float64(height)*scale)))
+}
+
+func imageHasTransparency(img image.Image) bool {
+	switch m := img.(type) {
+	case *image.YCbCr:
+		return false
+	case *image.Gray, *image.Gray16, *image.CMYK:
+		return false
+	case *image.NRGBA:
+		for i := 3; i < len(m.Pix); i += 4 {
+			a := m.Pix[i]
+			if a != 0xff {
+				return true
+			}
+		}
+		return false
+	case *image.RGBA:
+		for i := 3; i < len(m.Pix); i += 4 {
+			a := m.Pix[i]
+			if a != 0xff {
+				return true
+			}
+		}
+		return false
+	case *image.Alpha, *image.Alpha16:
+		return true
+	}
+
+	b := img.Bounds()
+	for y := b.Min.Y; y < b.Max.Y; y++ {
+		for x := b.Min.X; x < b.Max.X; x++ {
+			_, _, _, a := img.At(x, y).RGBA()
+			if a != 0xffff {
+				return true
+			}
+		}
+	}
+	return false
+}
+
+func applyOrientation(img image.Image, orientation int) image.Image {
+	if orientation < 2 || orientation > 8 {
+		return img
+	}
+
+	b := img.Bounds()
+	w, h := b.Dx(), b.Dy()
+	dstW, dstH := w, h
+	if orientation >= 5 {
+		dstW, dstH = h, w
+	}
+
+	dst := image.NewRGBA(image.Rect(0, 0, dstW, dstH))
+	for y := 0; y < dstH; y++ {
+		for x := 0; x < dstW; x++ {
+			sx, sy := orientedSourcePoint(x, y, w, h, orientation)
+			dst.Set(x, y, img.At(b.Min.X+sx, b.Min.Y+sy))
+		}
+	}
+	return dst
+}
+
+func orientedSourcePoint(x, y, width, height, orientation int) (int, int) {
+	switch orientation {
+	case 2:
+		return width - 1 - x, y
+	case 3:
+		return width - 1 - x, height - 1 - y
+	case 4:
+		return x, height - 1 - y
+	case 5:
+		return y, x
+	case 6:
+		return y, height - 1 - x
+	case 7:
+		return width - 1 - y, height - 1 - x
+	case 8:
+		return width - 1 - y, x
+	default:
+		return x, y
+	}
+}
+
+func jpegOrientation(data []byte) int {
+	if len(data) < 4 || data[0] != 0xff || data[1] != 0xd8 {
+		return 1
+	}
+
+	for i := 2; i+4 <= len(data); {
+		if data[i] != 0xff {
+			i++
+			continue
+		}
+		for i < len(data) && data[i] == 0xff {
+			i++
+		}
+		if i >= len(data) {
+			return 1
+		}
+
+		marker := data[i]
+		i++
+		if marker == 0xd9 || marker == 0xda {
+			return 1
+		}
+		if marker >= 0xd0 && marker <= 0xd7 {
+			continue
+		}
+		if i+2 > len(data) {
+			return 1
+		}
+
+		segmentLen := int(binary.BigEndian.Uint16(data[i : i+2]))
+		i += 2
+		if segmentLen < 2 || i+segmentLen-2 > len(data) {
+			return 1
+		}
+
+		payload := data[i : i+segmentLen-2]
+		if marker == 0xe1 && bytes.HasPrefix(payload, []byte("Exif\x00\x00")) {
+			return tiffOrientation(payload[6:])
+		}
+		i += segmentLen - 2
+	}
+
+	return 1
+}
+
+func tiffOrientation(data []byte) int {
+	if len(data) < 8 {
+		return 1
+	}
+
+	var order binary.ByteOrder
+	switch string(data[:2]) {
+	case "II":
+		order = binary.LittleEndian
+	case "MM":
+		order = binary.BigEndian
+	default:
+		return 1
+	}
+	if order.Uint16(data[2:4]) != 42 {
+		return 1
+	}
+
+	ifdOffset := int(order.Uint32(data[4:8]))
+	if ifdOffset < 0 || ifdOffset+2 > len(data) {
+		return 1
+	}
+
+	entryCount := int(order.Uint16(data[ifdOffset : ifdOffset+2]))
+	pos := ifdOffset + 2
+	for i := 0; i < entryCount; i++ {
+		if pos+12 > len(data) {
+			return 1
+		}
+
+		tag := order.Uint16(data[pos : pos+2])
+		fieldType := order.Uint16(data[pos+2 : pos+4])
+		count := order.Uint32(data[pos+4 : pos+8])
+		if tag == 0x0112 && fieldType == 3 && count == 1 {
+			value := int(order.Uint16(data[pos+8 : pos+10]))
+			if value >= 1 && value <= 8 {
+				return value
+			}
+			return 1
+		}
+		pos += 12
+	}
+
+	return 1
+}
+
+func isSupportedImage(path string) bool {
+	switch strings.ToLower(filepath.Ext(path)) {
+	case ".jpg", ".jpeg", ".png":
+		return true
+	default:
+		return false
+	}
+}
+
+func copyFile(src, dst string, mode fs.FileMode) error {
+	in, err := os.Open(src)
+	if err != nil {
+		return err
+	}
+	defer in.Close()
+
+	if err := os.MkdirAll(filepath.Dir(dst), 0o755); err != nil {
+		return err
+	}
+
+	out, err := os.OpenFile(dst, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, mode)
+	if err != nil {
+		return err
+	}
+
+	if _, err := io.Copy(out, in); err != nil {
+		_ = out.Close()
+		return err
+	}
+	return out.Close()
+}
+
+func copySymlink(src, dst string) error {
+	target, err := os.Readlink(src)
+	if err != nil {
+		return err
+	}
+	if err := os.MkdirAll(filepath.Dir(dst), 0o755); err != nil {
+		return err
+	}
+	return os.Symlink(target, dst)
+}
+
+func clampJPEGQuality(q int) int {
+	if q <= 0 {
+		return 82
+	}
+	if q < 1 {
+		return 1
+	}
+	if q > 100 {
+		return 100
+	}
+	return q
+}
+
+func max(a, b int) int {
+	if a > b {
+		return a
+	}
+	return b
+}
+
+func FormatBytes(n int64) string {
+	const unit = 1024
+	if n < unit {
+		return fmt.Sprintf("%d B", n)
+	}
+	div, exp := int64(unit), 0
+	for n >= unit*div && exp < 4 {
+		div *= unit
+		exp++
+	}
+	return fmt.Sprintf("%.1f %ciB", float64(n)/float64(div), "KMGTPE"[exp])
+}

internal/pdfassets/pdfassets_test.go

@@ -0,0 +1,100 @@
+package pdfassets
+
+import (
+	"bytes"
+	"image"
+	"image/color"
+	"image/jpeg"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestFitWithin(t *testing.T) {
+	w, h := fitWithin(400, 200, 100, 100)
+	if w != 100 || h != 50 {
+		t.Fatalf("fitWithin landscape = %dx%d, want 100x50", w, h)
+	}
+
+	w, h = fitWithin(200, 400, 100, 100)
+	if w != 50 || h != 100 {
+		t.Fatalf("fitWithin portrait = %dx%d, want 50x100", w, h)
+	}
+}
+
+func TestApplyOrientationRightTop(t *testing.T) {
+	img := image.NewRGBA(image.Rect(0, 0, 2, 3))
+	for y := 0; y < 3; y++ {
+		for x := 0; x < 2; x++ {
+			img.Set(x, y, color.RGBA{R: uint8(x), G: uint8(y), A: 0xff})
+		}
+	}
+
+	got := applyOrientation(img, 6)
+	if got.Bounds().Dx() != 3 || got.Bounds().Dy() != 2 {
+		t.Fatalf("oriented bounds = %v, want 3x2", got.Bounds())
+	}
+	assertRGBA(t, got.At(0, 0), color.RGBA{R: 0, G: 2, A: 0xff})
+	assertRGBA(t, got.At(2, 1), color.RGBA{R: 1, G: 0, A: 0xff})
+}
+
+func TestPrepareTreeOptimizesImagesAndSkipsPDFs(t *testing.T) {
+	root := t.TempDir()
+	if err := os.MkdirAll(filepath.Join(root, "assets", "img"), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(root, "index.html"), []byte(`<img src="assets/img/photo.jpg">`), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(root, "old.pdf"), []byte("old pdf"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+
+	var src bytes.Buffer
+	img := image.NewRGBA(image.Rect(0, 0, 400, 200))
+	for y := 0; y < 200; y++ {
+		for x := 0; x < 400; x++ {
+			img.Set(x, y, color.RGBA{R: uint8(x), G: uint8(y), B: 120, A: 0xff})
+		}
+	}
+	if err := jpeg.Encode(&src, img, &jpeg.Options{Quality: 95}); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(root, "assets", "img", "photo.jpg"), src.Bytes(), 0o644); err != nil {
+		t.Fatal(err)
+	}
+
+	prepared, err := PrepareTree(root, Options{MaxWidth: 100, MaxHeight: 100, JPEGQuality: 70})
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer prepared.Cleanup()
+
+	if prepared.Stats.ImageFiles != 1 || prepared.Stats.OptimizedImages != 1 {
+		t.Fatalf("stats = %+v, want one optimized image", prepared.Stats)
+	}
+	if _, err := os.Stat(filepath.Join(prepared.Root, "old.pdf")); !os.IsNotExist(err) {
+		t.Fatalf("old PDF copied into prepared tree; err=%v", err)
+	}
+
+	out, err := os.Open(filepath.Join(prepared.Root, "assets", "img", "photo.jpg"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer out.Close()
+	cfg, err := jpeg.DecodeConfig(out)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if cfg.Width > 100 || cfg.Height > 100 {
+		t.Fatalf("optimized dimensions = %dx%d, want within 100x100", cfg.Width, cfg.Height)
+	}
+}
+
+func assertRGBA(t *testing.T, got color.Color, want color.RGBA) {
+	t.Helper()
+	r, g, b, a := got.RGBA()
+	if uint8(r>>8) != want.R || uint8(g>>8) != want.G || uint8(b>>8) != want.B || uint8(a>>8) != want.A {
+		t.Fatalf("color = rgba(%d,%d,%d,%d), want %+v", uint8(r>>8), uint8(g>>8), uint8(b>>8), uint8(a>>8), want)
+	}
+}